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46 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. element name=AbstractFeature type=gml:AbstractFeatureType abstract=true substitutionGroup=gml:AbstractGML This abstract element serves as the head of a substitution group which may contain any elements whose content model is derived from gml:AbstractFeatureType. This may be used as a variable in the construction of content models. gml:AbstractFeature may be thought of as ―anything that is a GML feature‖ and may be used to define variables or templates in which the value of a GML property is ―any feature‖. This occurs in particular in a GML feature collection see 9.9 where the feature member properties contain one or multiple copies of gml:AbstractFeature respectively.

9.4 Standard feature properties

9.4.1 boundedBy, BoundingShapeType, EnvelopeWithTimePeriod, EnvelopeWithTimePeriodType

This property describes the minimum bounding box or rectangle that encloses the entire feature. Its content model is as follows: element name=boundedBy type=gml:BoundingShapeType nillable=true complexType name=BoundingShapeType sequence choice element ref=gml:Envelope element ref=gml:Null choice sequence attribute name=nilReason type=gml:NilReasonType complexType The gml:Envelope element is defined in 10.1.4.6. A nil value shall be encoded as described in 8.2.3.2. The attribute nilReason may be used in such cases to specify the reason for the nil value. The value of gml:Null, used in previous versions of GML to encode that an extent is not applicable or not available for some reason, has been deprecated. NOTE 1 Since an envelope is defined simply by the positions of two diagonally opposing corners, the exact footprint of an envelope depends on the coordinate reference system used. If the feature being described has zero extent, then the two corners will coincide and the envelope has zero size. The gml:boundedBy property is provided by a data supplier for convenience. The value of the envelope is usually computable by the data consumer from the spatio-temporal properties of a feature. As for all properties, it is the responsibility of the data provider to ensure that the value is correct. For envelopes that include a temporal extent, gml:EnvelopeWithTimePeriod is provided, defined as follows: element name=EnvelopeWithTimePeriod type=gml:EnvelopeWithTimePeriodType substitutionGroup=gml:Envelope complexType name=EnvelopeWithTimePeriodType complexContent extension base=gml:EnvelopeType sequence element name=beginPosition type=gml:TimePositionType element name=endPosition type=gml:TimePositionType sequence